Transmitting television (TV) and video on demand signals over the Internet is becoming more and more common. A number of commercial services already exist. IPTV (Internet Protocol Television) describes a system where a digital television service is delivered to subscribing consumers using the Internet Protocol over a broadband connection, e.g. the widely used xDSL connection. This service is often provided in conjunction with Video on Demand and is typically supplied by a broadband operator using the same infrastructure.
IPTV covers both live TV (multicasting) as well as stored video content (Video on Demand, VOD). The playback of IPTV requires either a personal computer device or a set-top box connected to a TV. Video content is typically delivered via IP Multicast, a method in which information can be sent to multiple computers at the same time. In standards-based IPTV systems, the primary underlying protocols used for IPTV are Internet Group Management Protocol (IGMP) version 2 for channel change signaling for live TV and Real Time Streaming Protocol (RTSP) for Video on Demand.
Wireless Local Area Networks (WLAN), Worldwide Interoperability for Microwave Access (WiMAX) and other radio technologies are used to provide wireless Internet access in homes, offices and hot-spots. Generally UDP based multicast/broadcast streaming protocols are used with video signals, as they work much more efficiently compared to the TCP protocol. Also multicasting is not possible with TCP; the re-transmission state machines have to be link specific, i.e. they can not be shared by a high number of receivers as required in video streaming applications. However UDP protocol inherits certain quality issues in wireless connections.
The User Datagram Protocol (UDP) is one of the core protocols of the Internet protocol suite. UDP is defined to make available a datagram mode of packet-switched computer communication in the environment of an interconnected set of computer networks. This protocol requires that the Internet Protocol (IP) is used as the underlying protocol. Using UDP, programs on networked computers can send short messages known as datagrams to one another. UDP does not provide the reliability and ordering that TCP guarantees. That is, datagrams may arrive out of order or even go missing without being noticed. In other words, packets are liable to be lost or corrupted in transit. However, as a result, UDP is faster and more efficient for many lightweight or time-sensitive purposes, as it has a reduced overhead compared to TCP. Therefore, and due to the fact that multicasting is possible with UDP in contrast to TCP, UDP is used in applications as IPTV.
In the UDP protocol packets are sent from the sender to the receiver without feedback about transmission success, that is, some acknowledgement scheme. If the receiver is unable to extract the correct information from the received packet there are no means provided to request a retransmission of the packet. Depending on the extent of the loss the client may be able to recover the data with error correction techniques, may interpolate over the missing data, or may suffer a dropout. In certain applications like Voice over IP a small amount of dropouts may be tolerable compared to time delays due to retransmitted data packets.
Typically in wired Ethernet network these properties of UDP are not a problem, as the transmission media is reliable and relatively insensitive to disturbances. In unmanaged radio connections (such as WLAN) the situation is different. The environment is hostile and the quality of radio links can vary due to a number of different reasons. In addition, the actual throughput is much lower than the theoretical peak bit rate, due to the overhead of lower layers, particularly the preamble needed for L1 synchronization. For these reasons WLAN and other radio technologies have severe quality issues in providing high quality video and IPTV services using the UDP protocol.
Typically the Internet infrastructure is implemented such that WLAN and other radio access technologies are used only for covering the final distance (like last tens of yards) inside a home, office or hot-spot. Connections to radio access points in turn are typically made with xDSL, optical or other wire-based technologies. In prior art situations IPTV terminals are connected to xDSL modems via wire-based Ethernet connections. It would be advantageous to be able to replace such wired connections by WLAN or similar wireless connections, as to these are already widely used in small home or office networks connecting PCs, laptop computers and even PDAs with the Internet in the house or office.
However, the above mentioned problems with IPTV originate from a scenario wherein a WLAN connection shall be used in the Internet connection for IPTV. In contrast to cable connections, wireless connections are less reliable and prone to errors due to signal attenuation, interference generated by other devices using the same un-controlled radio band and multi-path propagation or channel variation, e.g. when the user carrying a portable IPTV playback device is moving around. The UDP protocol that is used in IPTV, however, expects a reliable connection and therefore doesn't provide acknowledgement of received packets. Consequently, packet retransmission is not provided for. Prior art solutions add redundancy to the transmitted signal to recover disturbances. This is done in form of forward error correction and interleaving the TV data over multiple IP packets. This however reduces the throughput capacity of the system. As a native MPEG-2 stream may already require most of e.g. a 8 MBit/s ADSL link, there is not left much reserve capacity for such error correction schemes.
It would be beneficial if IPTV terminals could be connected using a wireless technology such as WLAN as well, but without being subjected to the data corruption which is likely in the combination of WLAN and UDP based video transmission. This would enable wireless access connections to be used also for UDP based TV and video broadcast streams. It could help reduce the expensive cabling which would otherwise be required in homes and offices.
Therefore it is an object of the present invention to provide methods and devices for reliably relaying UDP-based (and probably also multicast) IPTV over wireless IP networks using point-to-point links. The invention may also enable the use of existing IPTV playback hardware/software and be interoperable with existing IPTV providers using broadband Internet connections.